System.Net.Mail seems like a pretty stable class of email objects. There are
a few known issues. I'm sure more will crop up over time. At the time I put this
FAQ together, System.Net.Mail has been out of beta for less than 30 days. Check
the forums for more ideas and help.

If you do get any exceptions, be sure to always check the inner
exception for more additional information. Usually the inner exceptions will
provide the additional information to solve your problem. Here's a code example
for checking inner exceptions in a console application. If you want to use this
code in an ASP.NET page, be sure to change Console.WriteLine(...) to
Response.Write(...).